1. Field of the Invention
The present invention relates to an image lens array for a small image taking device, and particularly to a mid-aperture type image lens array consisted of three plastic lenses that are provided with aspherical surfaces.
2. Description of the Prior Arts
Since the image pick up lens has an increasingly wide range of application, plus the consumer electronic industrial is growing fast, the small image pick-up lens is accordingly found in great demand in different fields, particularly in photographic cell phone, digital camera, or auto's detection system for parking or other purposes.
A photosensitive element for a digital fixed focus lens array generally includes charge coupled device (CCD) type or CMOS type Complementary Metal Oxide Semiconductor, and its light sensitivity will be reduced sharply with the increase of exit angle of the lens. Therefore, the digital fixed focus lens array is usually provided with telecentric type for prevention of shading problem. However, most of the existing over Megapixel lens arrays are consisted of 3-4 lenses approximately 5.5-7 mm high, these types of lens arrays still have some technical defects as follows:
First, the exit angle of over Megapixel lens array should be reduced, considering the brightness, so that the optical system needs a large space to refract light. Since most of the aforementioned optical systems are 5.5-7 mm high (cannot be reduced further), even if the future pixel is further minimized as a result of further advancement of semi-conductor technology, the resolution of the optical systems should be high, thus causing difficulties in making a handy and light lens array.
Second, most of the conventional digital fixed focus lens array employ front aperture to correct aberration, however, the front aperture arrangement will lead to an increase both in stray light and sensitivity of the optical system, substantially complicating the design process.
U.S. Pat. No. 6,441,971B2 discloses a small image lens array with large aperture (f/2.5), the specification of the photosensitive element is ¼ inch while the total length of the image lens array is up to 5.3 mm. As for the existing small image lens array, every 0.1 mm reduction in the total height of the lens array will lead to a substantial degradation of the resolution quality.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.